Shock absorbers are used in conjunction with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the vehicle.
The most common type of shock absorbers for automobiles is the dashpot type which can be either a mono-tube design or a dual-tube design. In the mono-tube design, a piston is located within a pressure tube and is connected to the spring mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the pressure tube into an upper working chamber and a lower working chamber. The piston includes compression valving which limits the flow of damping fluid from the lower working chamber during a compression stroke and rebound valving which limits the flow of damping fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. Because the compression valving and the rebound valving have the ability to limit the flow of damping fluid, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass.
In a dual-tube shock absorber, a fluid reservoir is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. A base valve assembly is located between the lower working chamber and the fluid reservoir to control the flow of dampening fluid. The compression valving of the piston is moved to the base valve assembly and is replaced by a compression check valve assembly. In addition to the compression valving, the base valve assembly includes a rebound check valve assembly. The compression valving of the base valve assembly produces the damping force during a compression stroke, and the rebound valving of the piston produces the damping force during a rebound or extension stroke. Both the compression and rebound check valve assemblies permit fluid flow in one direction, but prohibit fluid flow in an opposite direction; however, they are designed such that they do not generate a damping force.
The valving for the shock absorber which determines the damping loads whether it is part of the piston assembly or the base valve assembly typically comprises one or more valve discs which is/are clamped or otherwise urged against a hub land by some type of a retainer. When the inner portion of the valve disc is clamped or urged against the hub land, the outer portion of the valve disc is biased against an outer land. The assembly of the valve discs against the lands defines flow restriction contours by means of the achieved interaction with the bending of the valve disc or the valve disc stack.
In order to control the flow restriction contours it is necessary to accurately control and measure the contour of the lands. Conventional or prior art measurement methods consist of a tool which has a reference surface which locates on the outer land and a dial type gauge with a flat probe which then measures the hub land. The measured values obtained by this prior art tool by locating the reference face of the measurement tool against the outer land provides an overall indication about the hub land in relation to the outer land but detailed information about the shape of the outer land is masked. Since the shape of the outer land is relevant to the control of the flow restriction contours, measurement of the outer land shape is needed.